Louisville Area Ozone: U.S. EPA Proposes LMP Approval, Comments Due September 17

What U.S. EPA Is Proposing

On August 27, 2026, U.S. Environmental Protection Agency (EPA) Region 4 published a proposed rule (91 FR 55294) to approve a revision to the Kentucky State Implementation Plan (SIP) consisting of a Limited Maintenance Plan (LMP) for the Kentucky portion of the bi-state Louisville, Kentucky-Indiana 1997 8-hour ozone maintenance area. The Kentucky portion covers Bullitt, Jefferson, and Oldham Counties. Comments are due on or before September 17, 2026, under Docket ID No. EPA-R04-OAR-2024-0295.

The Energy and Environment Cabinet submitted the SIP on behalf of the Louisville Metro Air Pollution Control District on June 3, 2024. If finalized, the action would make certain maintenance-related commitments federally enforceable as part of the Kentucky SIP.

Louisville Area Attainment and the LMP Option

U.S. EPA designated the bi-state Louisville Area, the three Kentucky counties plus Clark and Floyd Counties in Indiana, as nonattainment for the 1997 8-hour ozone National Ambient Air Quality Standard (NAAQS) on April 30, 2004, effective June 15, 2004. Kentucky submitted a redesignation request and first 10-year maintenance plan on September 29, 2006, and U.S. EPA redesignated the Kentucky portion to attainment effective August 6, 2007.

Clean Air Act (CAA) section 175A(b) requires a second maintenance plan eight years after redesignation, extending the demonstration to 20 years. U.S. EPA’s 2008 ozone implementation rule had concluded that revocation of the 1997 standard eliminated that obligation, but the U.S. Court of Appeals for the District of Columbia Circuit (D.C. Circuit) vacated that interpretation in South Coast Air Quality Management District v. EPA, 882 F.3d 1138 (D.C. Cir. 2018), reinstating the requirement for “orphan maintenance areas.” Kentucky’s submittal responds to that decision and is designed to maintain the standard through 2027.

Because monitored concentrations have stayed well below the standard, the Cabinet used the LMP option, a streamlined demonstration substituting evidence of low violation probability for modeling or projected-inventory analysis. LMP submittals must still include an attainment inventory, monitoring network provisions, and a contingency plan.

Attainment Inventory

The submittal presents a 2019 typical summer day attainment inventory alongside the 2003 inventory from the first maintenance plan. Emissions totals for nitrogen oxides (NOx) and volatile organic compounds (VOC) are shown in Table 1 in tons per summer day (tpsd).

Table 1
Attainment Inventory

County	NOx tpsd (2003)	NOx tpsd (2019)	VOC tpsd (2003)	VOC tpsd (2019)
Bullitt	10.04	5.77	16.95	19.74
Jefferson	170.76	62.59	80.61	63.05
Oldham	6.22	2.61	7.01	2.80
Total	187.02	70.97	104.57	85.59

NO_x emissions declined in all three counties, driven largely by on road, nonroad, and point source reductions in Jefferson County. VOC emissions declined overall, though VOC from point and nonpoint sources increased in Bullitt County while VOC from nonpoint sources increased but VOC from point sources decreased in Jefferson County. The 2019 inventory is based on information from the 2017 National Emissions Inventory, source-reported data under District Regulation 1.06 and 401 KAR 52:020 and 52:030, KIPDA travel demand modeling paired with MOVES3.0.3, and U.S. EPA’s 2016v2 platform. U.S. EPA concludes that the 2024 submittal includes a comprehensive and reasonably accurate inventory of actual ozone precursor emissions in attainment year 2019. According to U.S. EPA, the inventories are acceptable for the purposes of subsequent maintenance plan under CAA section 175A(b).

Air Quality Monitoring and Stability Trend

Under the rounding convention in 40 CFR part 50, Appendix I, the 1997 standard is attained at a design value of 0.084 ppm or below. Across the seven monitors in the bi-state Louisville Area, no design value exceeded the standard from 2013 through 2025, and U.S. EPA notes an overall downward trend at each monitor. All current design values fall below 85 percent of the standard except one Jefferson County monitor (AQS ID 21-111-0067), at 0.075 ppm, or 89 percent of the exceedance level.

The maximum design value increase over the last eight years was 0.008 ppm. U.S. EPA added this design value increase (0.008 ppm, at the Clark County, Indiana monitor) to the most recent maximum design value of 0.075 ppm. The 0.083 ppm result is below the 0.084 ppm threshold (1997 8-hour NAAQS) and air quality monitoring demonstrates that past air quality trends were shown to be stable, supporting a low probability of violation before the maintenance period closes in 2027. 

U.S. EPA is required to annually review the ozone monitoring network in accordance with 40 CFR Part 58. U.S. EPA approved Kentucky’s 2025 Ambient Air Monitoring Network Plan on October 28, 2025, and proposes to find the Cabinet’s network adequate to verify continued attainment of the ozone standard in the bi-state Louisville Area.

Contingency Measures and Potential Impacts to Facilities

A maintenance plan must include contingency measures to prevent future NAAQS violations or to promptly remedy any future NAAQS violations in accordance with CAA section 175A(d). Contingency triggers documented in the LMP to determine when control measures are needed include any 8-hour reading of 0.085 ppm or greater, or reported growth above 10 percent in NOx or VOC emissions over the attainment inventory. The Division for Air Quality will evaluate existing control measures and evaluate whether further measures are necessary to reduce emissions when triggering mechanisms are encountered. If additional controls are needed following the evaluation, then implementation of controls as a response to an initial “indicator” will be required as expeditiously as possible. If the fourth-highest monitored value of 0.085 ppm or greater occurs during an annual ozone season, then implementation of controls is required no later than 12 months following the end of the most recent ozone season (October 31). Additional coordination with state and local authorities is necessary if a violation of the standard occurs within the bi-state Louisville Area.

The updated LMP introduces incentive programs for engine idling reduction and fleet diesel retrofits while removing earlier proposals for downtown peak-period vehicle restrictions. Other key contingency measures include evaluation of further controls such as Reasonably Available Control Technology (RACT) for point sources of VOC and NO_x covered under Control Techniques Guidelines Groups II, III, and IV and implementation of a program to enhance inspection of stationary sources. Facilities should be aware that enhanced inspection programs may lead to more rigorous and frequent inspections of stationary sources of combustion emissions and stationary sources emitting VOC. Additionally, Facilities with large vehicle fleet operations should be aware of incentives available if diesel retrofit programs are implemented.

For more information about the LMP, please see 91 FR 55294 published on August 27, 2026. Beyond the Louisville area, a companion proposal published the same day (91 FR 55300) addresses the Northern Kentucky portion of the tri-state Cincinnati-Hamilton area — Boone, Campbell, and Kenton Counties.

ALL4’s Kentucky-based staff are tracking these and other regulatory proposals and can help you strategize around projects and emissions reduction opportunities. Contact Dan Hardin at dhardin@all4inc.com with questions about how this proposal could affect your facility.